docs: def collapse_to_genes(graph):
      """Collapse all protein, RNA, and miRNA nodes to their corresponding gene nodes.
  
      :param pybel.BELGraph graph: A BEL graph
      """
      enrich_protein_and_rna_origins(graph)
      collapse_dict = _build_collapse_to_gene_dict(graph)
      collapse_nodes(graph, collapse_dict)